CMake Error at __cmakepp.cmake:15936 (endforeach):   Flow control statements are not properly nested. Call Stack (most recent call first):   install.cmake:17 (include)

```
curl -OL https://raw.github.com/toeb/cmakepp/master/install.cmake && cmake -P install.cmake && rm install.cmake
```

on macOS 11.4 (20F71) with cmake version 3.21.2